Alkaline detergent



Patented Dec. 1,1942

2.303.397 V ALKALINE DETERGENT Charles Schwartz, Pittsburgh, Pa, assig'nor to Hall Laboratories, Inc., Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application May 1, 1939,

' Serial No. 271,176

8 Claims. -(Cl. 252-135) This invention relates generally to alkaline preparations, for example alkaline detergents for cleaning soft metals and more particularly to such detergents containing alkali-metal silicates and an inhibiting agent for preventingthe alkaline corrosion of the metal.

' It is a well known fact that many highly alkaline detergents while performing excellently as cleaners can not be used for cleaning soft metals such as aluminum and tin, since the alkalides corrode and dissolve the metals quite readily.

Many efforts have been made to utilize the excellent detergent properties of highly alkaline mixtures and at the same time to prevent, in so far as possible, the attack upon soft metals. Thus the use of certain silicates has been successful in decreasing to a considerable extent the corrosion of aluminum in alkaline solutions. It is necessary, however, to be very careful in the choice of silicate used and in the concentration of the solution in order to avoid very serious attack upon the metal being washed. If the concentration of the solution is too high or too low, it attacks the aluminum and this places a serious limitation on the type of solution which may be employed.

silicates have been used also for cleaning tin but in this case the alkalinity of the cleaning solution must be adjusted to so low a pH and the temperature dropped to such an extent that effective cleaning can not easily be obtained. Other remedies for the corrosion of tin and aluminum by alkaline cleaners have been suggested also. In the case of tin, the use of sodium sulphite has become quite widespread in recent years. This material decreases the oxygen concentration of the cleaning solution and inhibits the corrosion of tin by alkalies. However, there is considerable corrosion after the sulphite is v v depleted, as it is very shortly in usual practice.

Where the solution is heated in contact with air,

the sodium sulphite is readily converted into sodium sulphate, which is ineffective in preventing corrosion.

Probably the most successful remedy for corrosion which has been found thus far has been the addition of chromates or dlchromates to alkaline materials in the washing'of soft metals; While in general these materials are quite successful in preventing corrosion, they have two serious drawbacks. They tend to coat the metal being washed with a greenish yellow film which in most cases is very undesirable. Most people are sensitive to chromates and the operators using the cleaners frequently suffer from what is known as chromiculcers, which necessitate cessation of all work with material containing chromates and which require long periods of time for healing.

It is an object of the present invention to provide means by whichalkaline detergents may be made safe for cleaning soft metals. The present invention has many advantages over the methods previously employed. Aluminum, tin,

zinc, lead, cadmium or other soft metals or al-.

loys thereof may be treated with solutions of extremely high pH at boiling temperatures for long periods of time without showing any evidence of corrosion. The cleaning solutions preferably have a pH of at least 10 and in many cases the pH is as high as '12 or over. The corrosion inhibitors which I employ do not decrease in effectivenesswith time, as do the sulphltes, but remain effective over long periods. They are without harmful effect upon the human skin and will not occasion the difficulties accompanying the use of chromates or dichromates.

I have found that the water-soluble salts of barium and strontium when added in proper proportion to alkali-metal silicates or to a mixture of alkaiiescontaining an alkali-metal silicate as its principal alkaline ingredient prevent entirely the characteristic corroding effect of these silicates. The mechanism whereby the corrosion is prevented is unknown but it probably can be ascribed to the formation of nonreactive protective films on the metal surfaces.

Sodium metasilicate, sesquisilicate and orthosilicate are strong alkalies, their alkalinity increasing in the order listed. It is well known that even the weakest of these, namely sodium metasilicate when used for example to wash tin or tin plate causes rapid spangling and solution of the tin even at relatively low temperature. I have found that by adding a small quantity of a water-soluble barium salt to any of these silicates the corrosive effect ofthe solution subsequently made from it is reduced to zero even at boiling temperatures over long periods of time. The following table, for example, indicates the results that have been obtained when several pieces of tin plate were boiled in solutions of sodium metasilicate with and without the addition of barium chloride as a typical water soluble barium salt.

TABLE 0.5% aqueous solution of sodium metasllicate metasilicate+5% barium chloride (based on weight of sodium metesllicate) biihl see aw-s Q a-aroma QQQOOCOO 0.5% aqueous solution of sodium tion for an hour. 1

It will be seen from the table that the solution containing the barium chloride did not cause any loss in weight of the tin even after boiling for 35 hours, whereas the solution not containing the barium salt caused a loss in Weight of 17.6 mg.

Strips of aluminum immersed for 22 hours in a 2% aqueous solution of sodium orthosilicate at 60 0. showed definite darkening and attack by chloride based on the weight of the sodium metasilicate showed no weight loss whatsoever.

While barium chloride has been referred to in the examples as a typical water-soluble barium salt which inhibits the corrosion of the metal, I

may employ any barium salt which is ordinarily soluble in water. Among the water soluble barium salts which may be used are barium chloride, barium nitrate, bariumhydroxide and barium formate. I have found that the nitrate and hydroxide work substantially as well as the chloride ininhibiting the corrosion of the metal. The amount of barium salt best suited for the purpose will depend upon the metal to be treated, thetreating solution and the conditions of treatment. Ordinarily the barium salt should be used in an amount equal to at least 2% based on the weight of thealkali-metal silicate. Generally it will be between 3% and 10%, although more might be used without harmful eifect. When the cleaning solution is used at low temperatures, it is possible to decrease the amount of barium salt even below the lowest figure previously given. Ordinarily, however, it is unnecessary to use more than 10% of the barium salt.

The silicate solution containing the corrosion inhibitor is useful in all cases where a, highly a1- kaline detergent is required. It may be used for example in the washing of tin plate, tubes, bakery pans, milk cans, and in tin fabricating plants. In the fabrication of tin plate, or articles made therefrom, it is. often necessary to apply grease to aid in the forming operations. This may be removed by the use of a highly alkaline cleaning solution in accordance with the present invention without attack on the tin. The cleaning solutions may be used also in the treatment of aluminum. In this case also, the solution may be used to remove the grease employed in fabricating the aluminum without, however, causing alkaline corrosion of the aluminum.

For washing pans in a bakery where the pans are washed fairly frequently, so that the amount of burned on matter is not excessive, I may use a cleaning composition containing about 95% sodium metasilicate and 5% barium chloride or other water-soluble barium salt. This is dissolved in water to form a solution of a strength between A of 1% and 3%. Sodium metasilicate, sesquisilicate or orthosilicate are generally employed in 1% solutions. In cleaning the bakery pans, they might be boiled in the cleaning solu- Where the deposits on the bakery pans are excessive, I might use an aqueous solution of a composition containing 95% sodium orthosilicate and 5% barium chloride or other water soluble barthe metal in the absence of silicates.

ium sea and boil the pans for an hour in that solution of a composition containing 60% sodium ,metasilicate, sodium hydroxide and.5% of barium chloride or other water-soluble barium salt where a highly alkaline solution is desired. I might add to this or'to the other compositions, a wetting agent such as a sodium salt of a sulphated fatty alcohol in the amount of 13%,

based on the total weight of the solids.

The barium salts also act as inhibitors in the presence of mixtures of silicates with sodium hydroxide or other alkalies, soap, casein, deflocculating agents wetting agents, abrasives and the like.

[I have found that the presence of silicate is necessary for the action of the barium ininhibiting corrosion but that it is possible to add other alkalies to the silicates. A 1% solution of trisodium orthophosphate corrodes' tin at boiling temperature in three minutes. Even if barium chloride is added to such solution,i t does not prevent corrosion of the tin, irrespective of the amount of barium chloride added. Tests have been made by adding 1%, 2%, 3%, 5%, 10%, 20% and 40% of barium chloride based on the weight of the trisodium orthophosphateand it was found that none of the 1% solutions made from these compositions prevented the corrosion of the tin.

Similar tests using alkali-metal carbonates as the alkaline materials have shown that the inhibitors are ineffective in preventing corrosion of The inhibitors to be effective must be used in a composition containing at least 50 of an alkali-metal silicate, although the amount of silicate required 'must be determined in each case and depends upon the nature of the,materials added to it and the conditions under which the mixture is to be used.

I have found that in all cases itis necessary that the alkaline solution contain an alkali-metal silicate as its principal alkaline ingredient, in order for the inhibiting agent to be effective. The-composition from which the cleaning solution is mademay contain other alkalies than conditions it may be increased. For example, if

the detergent contains sodium metasilicate and trisodium orthophosphate and is to be used in cleaning tin by heating the tin for one hour at boiling temperature, the metasilicate being used in a 1% solution, I could use about 5% of the trisodium orthophosphate based on .the weight of the metasilicate. "Ihe proportion of trisodium phosphate could be increased under less. severe conditions or if a less alkaline material than tri sodium orthophosphate was employed, I might use alarger proportion of it.

The statements made with reference to the inhibiting eflect of barium .saltsjhold true also Although scribed particularly 'will prevent the attack of the adhesive for the water-soluble strontium sal except that the strontium salts are somewhat less eifective in mixtures containing large amounts of sodium hydroxide or alkalies other than the silicates than are the barium salts.- Although I prefer to use strontium chloride} may use the nitrate or other water-soluble salt. The strontium salts are used in substantially the same proportions as those given for the barium salts and I have found that their effect is substantially identical to that of the barium salts except as above noted in the case where large amounts of sodium hydroxide are added to the alkali-metal silicate. Just as salts, together with the alkali-metal silicates, and also soap. casein,

of a metal of the group consisting of barium and strontium.

2. An alkaline detergent composition for soft metal, comprising by weight'about 95% sodium orthosilicate and about 5% of a water soluble salt of a metal of the group consisting of barium and strontium.

3. An alkaline detergent composition for soft metal, comprising metasilicate, about 35% sodium hydroxide and about 5% of a water soluble salt of a metal of I v the group consisting of barium and strontium.

in the case of compositions containing barium salts l may use strontium "4. An alkaline detergent composition for soft metal, comprising by weight about60 to 95% sodium metasiiicate, an eifective amount up to about 35% of sodium hydroxide, and an eifective deflocculating agents, wetting agents, abrasives and the like.

The invention enables the use of highly alkaline solutions containing alkali-metal silicates in the cleaning of soft metals without corrosion of the metal. Although the invention/has been dein. connection with preventm! the corrosion of plicable also to the treatment of zinc, lead, cadmium or other soft metals or alloys thereof. The term "soft metal" as used therein is intended to include any metal or alloy which under the proper conditions of temperature and concentration tends to be attacked or dissolved by alkaline solutions.

Although the principal use of the invention is aluminum and tin, it is apin connection with cleaning solutions, the invention is applicable to inhibiting corrosion of for example as paints or adhesives. The addition of a. water -soluble salt of barium or strontium to a silicate-containing paint or adhesive or paint on soft metals during the time required for thepaint or adhesive to set or harden.

The invention is'not limited to the examples, which have been given merely for illustrative purposes, or to the preferred proportions, butmay be otherwise embodied or practiced within the scope of the following claims.

Iclaim:

1. An alkaline detergent metaL-comprising by weight metasilicate and about 5% of composition for sort a water soluble salt about 05% sodium amount up to about 10% of..a water soluble salt of a metal of the group consisting of barium and strontium.

5. An alkaline detergent composition for soft metal, comprising by weight about to sodium metasilicate, an effective amount up to about 35% cf sodium hydroxide, and about 2% to 5%-of a water soluble salt of a metal of the group consisting of barium andstrontium.

6. An alkaline detergent composition for soft metal, comprising by weight about 60 to 95% of an alkali-metal metssilicate, an effective amount up to about 35% of an alkali-metal hydroxide, and an efiective amount up to about 10% of a water-soluble salt of a metal of the group consisting of barium and strontium.

'1. An alkaline detergent composition for soft metal, comprising by weight about 60 to 95% alkaliqmetal, metasilicate, an effective amount up to about 35% of an alkali-metal compound which is more alkaline than said alkali-metal meta-- metal of the group consisting of barium and strontium.

; CHARLES ECHWAR'I'Z.

by weight about 60% sodium 

